Ok, so after about a weeks time I revisited my 2x500 long axis extended tune up only this time I'd mark times, avg spl and over all perceived effort and execution.
And this time, like Terry, I had a couple of "miscues", taking one extra length of FR instead of BK on the first 500 and extra BK length on the second 500.
I discovered, as Terry did, that the 'confusion' came at the 300yd mark when the set broke into 50s of each stroke.
I didn't stop the swim however, I'd just mark time as is and adjust according to my average pace per 25 of each stroke.
On the first 500 I marked 8:17. Now, that had an extra length of FR, so I noted to add perhaps an extra 8-10sec calculating my avg time per 25 length of BK was approx 28/30sec with turn and approx 21/23 sec per length of FR ; @ 15spl BK and 15spl FR.
On the second go I felt a bit awkward at transition turns and did almost all open turns at transitions and between back lengths.
I did two extra lengths of BK and came in almost exactly one minute slower.
After some recovery lengths to clear the slate, I decided to do a repeat of the set beginning with 100 BK.
Still some trouble on BK turns but completed successfully @ same stroke counts and 8:40ish (forgot to stop my watch). Anyway quite a bit slower, a work in progress...
Finished up with some gears work, no formal set just trying to develop timing and a good hold as I move, cycling through recovery focus, kick timing, hip focus and hold/feeling a big arm full of water...